Experimental Survey of Lubricant-Film Characteristics and Oil Consumption in a Small Diesel Engine 910741
Parallel measurements of lubricant-film behavior and oil consumption in two identical small production IDI diesel engines are presented. Oil consumption was measured using tritium as a radioactive tracer, and instantaneous film thickness data between the piston and liner were obtained using laser fluorescence diagnostics. The data covered single- and multi-grade lubricants and five different ring configurations (two-piece vs three-piece rings at various ring tensions). The data illustrate (a) oil-film profiles under the rings, especially around the leading and trailing edges, (b) accumulation of oil on piston lands and skirt, (c) circumferential variations around the bore, (d) observations on ring rotation, and (e) the piston-skirt oil-pumping mechanism. Effects of lubricants and piston-ring configurations on oil-film characteristics are investigated, and the oil consumption data are compared with oil-film thickness measurements.
Radial tension appeared to have little effect on lubricant films on the piston lands for the two-piece oil-control rings; however, the effect was definitely present for the three-piece rings. The higher-tension ring allowed greater oil accumulation on the second land than the lower-tension ring at all speeds and operating conditions. Ring tension also affected little ring rotation rate, except for the three-piece rings, which appeared to require a threshold tension for rotation to occur.
The crown land was virtually dry on all four strokes of the engine cycle, and thus does not appear to contribute directly to oil consumption. Measured oil consumption rates differ substantially from calculated lubricant flows up and down the piston liner. However, similar to earlier results obtained on a heavy-duty diesel engine, current results indicate that two separate loops of oil transport may exist on the piston: a major loop that passes through the oil-relief holes under the oil-control ring, and a minor one on the upper piston lands that may play an important role in oil consumption.